1. Field of the Invention
The present invention relates to a communication apparatus which communicates with another apparatus in a power saving mode, a method of controlling the communication apparatus, and a storage medium.
2. Description of the Related Art
Recently, many wireless LAN devices complying with IEEE802.11 standard have been commercialized and used. IEEE802.11e standard supports Block Ack to improve the channel use efficiency on the physical layer. Block Ack is designed to collectively confirm receipt of a plurality of frames, unlike the prior art in which an Ack (acknowledgement) is returned in response to one frame. This technique allows to continuously transmit a plurality of frames instead of waiting for an Ack every time one frame is transmitted. In addition, IEEE802.11n standard supports aggregation, which is a technique of aggregating a plurality of MAC frames and transmitting them to implement high-speed transmission. A-MPDU (aggregation-MAC protocol data unit) which aggregates frames for each MPDU uses Block Ack to confirm receipt of each of aggregated frames. Using Block Ack allows to confirm receipt of aggregated MPDU subframes.
Recently, various kinds of product devices have been required to reduce power consumption. In order to reduce power consumption during a waiting time, some communication devices have a power saving mode designed to reduce power consumption by turning off blocks which are not associated with communication control until a request is issued from another communication device on the network. Such a communication device reduces power consumption by being set in the power saving mode during a waiting time, and switches to the normal mode, in which blocks other than a communication control unit are turned on, to execute predetermined processing in response to a request from another network device. In the power saving mode, since some circuits are turned off to reduce power consumption, limitations are imposed on the resources that can be used. In addition, to switch from the power saving mode to the normal mode, it is necessary to turn on another control unit. In some cases, therefore, it takes a predetermined time until the device switches to the normal mode.
When such a communication device receives an aggregation frame in the power saving mode, the device may lose frames. That is, if the storage area which can be used in the power saving mode is small, the device may not be able to store aggregation frames which are sequentially received. When receiving frames upon switching to the normal mode, it takes time to switch to the normal mode, and hence there is a chance that some aggregated frames will be lost during the switching time. Assume that Block Ack defined in IEEE802.11e is to be used. In this case as well, when a plurality of frames is continuously transmitted expecting Block Ack from the receiving side, there is a chance that the receiving side will lose frames.
Japanese Patent Laid-Open No. 2003-517741 discloses a technique of making a communication apparatus issue a request to enter the power saving mode to a base station before switching to the power saving mode so as to make the base station respond, on behalf of the communication apparatus, to a connectivity test message from another apparatus during the power saving mode.
Japanese Patent Laid-Open No. 2006-238320 discloses a technique of taking the statistics of the histories of time information of data frames received by a communication apparatus and deciding, based on the statistics result, whether the communication apparatus operates in the power saving mode.
In some cases, however, when an aggregation frame is transmitted or frames are continuously transmitted to a communication apparatus in the power saving mode, frame loss occurs.
In consideration of the above problem, the present invention provides a technique of reducing the loss of an aggregation frame or frames continuously transmitted while allowing an apparatus which is to be set in the power saving mode to maintain the power saving mode.